There exists a chemical vapor deposition (CVD) process for forming film on a surface of a single substrate (an object substrate having fine patterns of electrical circuits formed thereon with a silicon wafer or glass as a base) in a semiconductor manufacturing process. In the CVD process, a substrate is loaded into an airtight reaction chamber and heated by a heater provided within the reaction chamber to cause a chemical reaction while film forming gas is being introduced onto the substrate, so that film can be uniformly formed on fine patterns of electrical circuits formed on the substrate. According to such a CVD process, for example, organic chemical material may be used as film forming raw material to form a high-k film, such as a HfO film or the like, which is an insulating film having a high dielectric constant.
Since a HfO film formed in this way contains a considerable amount (i.e., several percentages) of impurities such as CH, OH or the like due to the organic chemical material, it has insufficient electrical insulating property. In order to secure sufficient electrical insulating property and stability of such a film, attempts have been made to reform the HfO film into a densified and stable film by subjecting the HfO film to a fast annealing treatment at about 650° C. to 800° C. under an O2 or N2 atmosphere, thereby removing impurities such as C, H and the like from the film. Such densification is performed to shorten the average interatomic distance in an amorphous state, although it does not lead to crystallization. Such a fast annealing treatment heats the entire substrate to a predetermined temperature to reform the HfO film.
In recent years, semiconductor devices may have a shallow junction structure with miniaturization and require a low thermal budget (thermal history). Accordingly, the annealing treatment used in the above-described high-k forming process requires removal of impurities from the film at a low temperature for film densification in order to provide a low thermal budget. The reason for the low temperature annealing treatment is as follows. Generally, in a process of manufacturing a device, if the device is treated in a later step at a temperature higher than that used in an earlier step, the device already built up in the earlier step may collapse or a film thereof may change in its characteristics. Therefore, the device cannot be treated in the later step at a temperature exceeding that used in the earlier step. Accordingly, there is a demand for a technique which can perform a film reforming process for improved device performance at a low temperature.
Japanese Patent Application Laid-Open Publication No. 2004-296820 discloses a technique in which, in a film depositing process, a hafnium-containing thin film is formed on a substrate, and, in a film reforming process, argon radicals are supplied onto the substrate so as to remove impurity elements contained in the thin film formed in the film depositing process.